Lsqfit

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Clean up Cython code. Adds lsqfit.fake_fitargs for testing. Bug fix in
nonlinear_fit.set() where resetting the fitter could cause crashes.

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Fixes trivial problem with the pyproject.toml introduced in the last version.

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Modified so that it works with numpy>=2.0.

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Same as v13.2.1.
- Fixes bug in lsqfit's GSL module that prevented compilation on some systems.

- Fixes minor bug in vegas_fit affecting parameter nitn.

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- Adds vegas_fit.sample, which samples the PDF used in the fit. This is useful for
making probability density histograms and contour plots.

- Minor bug fix: vegas_fit wasn't always passing correct arguments to PDFIntegrator.

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Adds a second least-squares fitting strategy. lsqfit.vegas_fit uses PDFIntegrator
from the vegas Python module to evaluate means, covariances, PDF histograms, etc
using Bayesian integrals, as opposed to minimization as in lsqfit.nonlinear_fit.
Fits from nonlinear_fit are Gaussian approximations to the results from
vegas_fit.